On the left an example of an accessory muscle at the dorsum of the wrist (T1- and T2-weighted).
Under the marker is a well-defined mass, iso-intense to normal muscle.
It is a muscle at mid-carpal level, with normal signal.
Normally, at this level, there is no muscle on the extensor side of the wrist, just tendon.
This is an accessory extensor digitorum manus brevis.
A recent article in Radiographics lists the accessory muscles in the human body (Sookur PA et al. Accessory Muscles: Anatomy, Symptoms, and Radiologic Evaluation. Radiographics 2008;28:481-499).
Dichlorodifluoromethane-trichloromono-fluoromethane is a nontoxic, nonflammable vapor coolant spray that does not irritate the skin but is no longer commercially available for other purposes because of its effect in reducing the ozone layer. However, its use is safer for both patient and physician than the original volatile vapor coolant, ethyl chloride. Ethyl chloride is a rapid-acting general anesthetic that becomes flammable and explosive when 4 to 15 percent of the vapor is mixed with air. 10 Nevertheless, ethyl chloride remains a popular agent because of its local anesthetic action and its greater cooling effect than that of dichlorodifluoromethane-trichloromonofluoromethane. 5